1. Field of the Invention
The present invention relates to a multilayer electronic component.
2. Description of the Related Art
In recent years, a demand for miniaturization of electronic parts associated with the high densification of electronic circuits used in digital electronic devices such as mobile phones has increased, and the miniaturization and capacity enlargement of multilayer electronic components constituting the circuits have been rapidly advanced.
For example, a plurality of internal electrodes is arranged in a ceramic sintered body in a multilayer electronic component such as multilayer ceramic capacitor.
To increase use efficiency of electrode materials, electrostatic capacity, accuracy, or the like, Patent Document 1 proposes a multilayer ceramic capacitor having no structure of side gaps. However, this capacitor has a problem in low voltage endurance, since internal electrodes are exposed to side surfaces of a ceramic sintered body.
Patent Document 2 proposes a structure capable of increasing voltage endurance. That is, a ceramic sintered body where internal electrodes are exposed to a pair of side surfaces is obtained, and side end edges of the internal electrodes are thereafter removed by a physical method such as etching and sandblasting. Then, synthetic resin, such as epoxy resin, is injected to the removed area to form insulating layers. This is how voltage endurance is improved.
However, if glass is used for the insulating layer, adhesion between the end surfaces where the internal electrodes are exposed and the glass tends to be weak. Thus, there is a problem in generation of cracks due to stress caused by differences in thermal expansion coefficient between the ceramic sintered body and the glass.
Furthermore, Patent Document 3 proposes a method for manufacturing a ceramic sintered body coated with insulating layers whose main component is glass, which is deposited on outer surfaces of a ceramic sintered body because a ceramic component of the ceramic sintered body contains a glass component at a predetermined weight ratio.
In this method, however, a thermal expansion coefficient of the ceramic sintered body is decreased, and almost no compression stress is applied to the insulating layer due to containment of glass as ceramic component. There is thus a problem that tensile stress from the ceramic sintered body to the insulating layer generated by thermal shock cannot be reduced and cracks are easy to be generated.
Patent Document 4 discloses a method for decreasing a thermal expansion coefficient of a non-capacitance portion containing barium titanate etc. by 4 to 10×10−7/K than a thermal expansion coefficient of a capacitance portion. This makes it possible to apply compression stress to the non-capacitance portion, reduce the tensile stress due to deflection, and enhance bending strength.
However, if glass is used for a non-capacitance portion, there is a problem that compression stress generated by the difference in thermal expansion coefficient is almost reduced due to low elastic modulus of glass, compression stress applied to the non-capacitance portion is not sufficient, and the effect of improving thermal shock resistance cannot be obtained.
In addition, there is a potential problem that thermal shock resistance glass is weak against tensile stress. For example, the following problem arises: If glass surface is scratched, tensile stress tends to concentrate on the scratched portion, and mechanical strength is decreased. Thus, the glass cannot bear thermal shock generated by soldering at the time of mounting, and cracks are easy to occur.
Also, there is a large problem in reliability because moisture resistance and withstand voltage may be decreased if cracks caused by stress of thermal shock are generated to not only a ceramic sintered body but also to glass of an insulating layer.
Patent Document 1: Japanese Examined Patent Publication No. H2-30570 B2
Patent Document 2: JP H3-82006 A
Patent Document 3: JP H11-340089 A
Patent Document 4: JP H11-340083 A